Weight stack frame



FIG. 1 is a side elevational view of a weight stack frame showing our new design, wherein the broken line showing of the weight stack and exercise machine is for illustrative purposes only and forms no part of the claimed design;

FIG. 2 is a rear perspective view of the weight stack frame;

FIG. 3 is a front view thereof; and,

FIG. 4 is a top plan view thereof. 

The ornamental design for a weight stack frame, as shown. 